Isabella de la Houssaye never saw her lung cancer coming.
The mom of five had never smoked a day in her life, didn’t drink and spent her spare time training for marathons, Ironmans and more. She was so active — and fast, winning her age group in a half marathon just a month before her diagnosis — that de la Houssaye, 54, assumed the severe pain she was experiencing was a running injury, not cancer.
“When I got symptoms last fall, everyone thought it was a sports injury, that I was overdoing it and it was overuse, which actually delayed the diagnosis,” she tells PEOPLE. “I was so active, and it was a good thing and a bad thing. If someone had said to me that lung cancer migrates to the spine, and then to the brain, I would have been more tuned into this level 10 pain that I was experiencing, but I didn’t know that.”
So de la Houssaye, from Lawrenceville, New Jersey, kept going, and even competed in an Ironman — which includes a 2.1-mile swim, a 112-mile bike ride and a 26.2-mile run — a month before her January 10th diagnosis.
“At that point it was stage 4 lung cancer,” she says. “I had a good size tumor, 7 centimeters, in my lungs. My entire sacrum [the pelvis] was cancer. I had six tumors in my brain, I had them in my sternum, I had them in my pelvis. It was a huge wake-up call.”
De la Houssaye started a targeted treatment in February, which managed to shrink the largest of the tumors in her brain and mostly heal her pelvis. And she worked with a physical therapist to rebuild her bones and strengthen them, especially her right leg, from which she had lost all movement prior to her diagnosis.
“Part of what I’m hearing for my doctors is that because I came in so strong and healthy, and that I continued to be, it helped my treatment,” she says. “It helps you tolerate the drugs.”
Over the last few months, de la Houssaye has slowly worked her way back to a point where she could walk — first with canes — and then run, getting up to 26 miles a day.
“Every day I got stronger and stronger,” she says. “It continues to amaze me how the body responds to the load you put on it.”
RELATED VIDEO: Paralyzed Man Plans to Run Half Marathon with Surgeon Who Gave Him 2% Chance to Walk Again
De la Houssaye then got a “gift” from the Ironman Foundation, in partnership with Ventum Racing — the opportunity to compete in the World Championship in Kona, Hawaii, a longtime dream of hers.
“We had this big plan that we would wait until my youngest turned 18, and then the whole family could all qualify together. It didn’t happen that way, but I’ve gotten this gift from the Ironman Foundation to compete, which is just a phenomenal opportunity,” she says.
“I’ve struggled a bit this month with the stress that I didn’t want to disappoint anybody, but I found this wonderful quote that I want to use to describe my story. It’s, ‘Failure is not defeat until you stop trying.’ to me, that’s the message, and I’m not going to stop trying, and I might not finish this race, but I’m going to give it everything I have. That’s the only thing I can do.”
And de la Houssaye will apply that same quote to as she continues treatment for her lung cancer.
“As of now, I am still stage 4 unfortunately,” she explains. “The drugs do not make the cancer go away; they just make it stop progressing. The nature of these treatments is that they work for a short while, about 18 months, and then the cancer mutates, so I will have a different cancer. So I can’t even look forward and ahead and prepare for that, because I’ll do a new biopsy, and we’ll just see what we’re dealing with and make a plan then.”
But de la Houssaye says she prefers not knowing.
“I find that that relieves me of the burden of having to think two steps ahead and lets me live in the day, and in this day I feel fabulous, and I’m so excited to be participating in this race coming up,” she says. “Much like running, I know that if I put one foot in front of the other I’ll keep going, and that’s the same with my treatment.”